This chapter is devoted to analysis of forced vibration of linear deformable elastic beams and frames with lumped and distributed masses, subjected to forced and kinematic excitation. The detailed analysis of the steady-state vibration of a deformable system with two degrees of freedom is considered. The particular importance of the dynamic systems with two degrees of freedom lies in the fact that it is these structures that make it possible to easily trace all the main stages of analysis characteristic of systems with a finite number of degrees of freedom, and to obtain analytical results. The continuity of classic analysis methods, such as the force and displacements methods, the initial parameters method, to dynamic problems of deformable systems is illustrated.
